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The Steem Blockchain is itself a database and a full copy of it is stored on every witness's machine. The developer can choose to access whichever part of that database they choose and display it or not. I could, for example, create a note-taking application that encrypted my notes, stored them on the blockchain, and then when I signed into the application I would only see the notes I uploaded in their decrypted form. I would be seeing only my data and no one else would be able to see it except in an encrypted form.

Awesome. Thanks for taking the time to awsner my questions